Process for the cementation of articles of iron, steel, and alloys of steel.



-mented are placed in -FEDERICO GIOLITTI, 0E TURIN, ITALY,

ASSIGNOR TO SOCIETA AN ON IMA IT-ALIANA GIO. ANSALDO ARMSTRONGK; (70., 0F GENOA, ITALY.

PROCESS FOR THE CEMENTATION OF ARTICLES OF' IRON, STEEL, AND ALLOYS OF STEEL.

1.093.844. Ili'oIDrawing'.

Specification of Letters Patent.

Patented Apr. 21, 1914.

Application filed June 13. 1910. Serial No. 566,576.

To all whom it may concern Be it known that I, Dr. Fnonnrco Gio- LITTI, a subject of the King of Italy, residing at No. 105 Corso Vittorio Emanuele, Turin. in the Kingdom of- Italy, have invented new and useful Improvements in Processes for the Cementation of Articles of Iron, Steel, and Alloys of Steel, of which the I following is a specification. I

This invention has for its object to pro- I vide an improved process for the cementation of articles of iron, steel and alloys of steel, whereby a layer of desired depth more I highly carburized than the remainder of the I article, may be produced in the zone situ- I ated immediately below the external surface of the article;

The improved process consists substantially in employing gaseous carbonic anhydrid (hereinafter referred to as carbon dioxid) in addition to carbon which 1s used n many existing cementation processes. I l

Carbon dioxid can be obtained in commerce in great purity and at a low price.

The employment of carbon. dioxid 1n the presence of wood charcoal or any other kind I of carbon, allows of dispensing entirely with I the use of the numerous foreign substances such as barium carbonate, alkaline cyanide, I ferrocyanids, nitrogeneous organic sub- I stances, hydrocarbids, etc., which it has I been neoessarv to add to wood charcoal in I the usual cementation processes in order to prevent the cementation from being practically useless by reason of its extreme slow- I ness. The improved process may be carried out I The articles to be cea fixed or movable rel ceptacle- (hereinafter referred to as the ceof steel plate or of re- I of form and dimensions varying with the nature and dimensions of the said articles. Inmany c ases small articles may be cemented in the ordinary re- I torts used in gas works for distilling coal l in the manufacture of illuminating gas. The cementing chamber is placed in a furnace capable of heating it to a constant and uniform temperature between the limits of l 900 and 1100 degrees centigrade. I The cementing chamber is provided with a door I capable of closing.- air-tight to allow of placing' the articles to'be cemented therein, and 3 generally as follows:

menting chamber ira ctory material with pipes arranged to cause. a current of carbon dioxid to circulate slowly through the chamber. The process is started by placing a layer of carbon in the cementing chamher. It is preferred for this purpose to use wood charcoal that has been thoroughly calcined and reduced to small pieces; this charcoal is hereinafter referred to as granulated charcoal. The size of the pieces of the granulated charcoal and the thickness of the layer of such charcoal vary accordlng to the varying dimensions, quantity and shape of the articles to be cemented. For instance for cementing at one operation 100 kilograms of pieces of steel not too complicated inshape, (such as for instance, ball bearing races, axles of bicycle wheels, etc.,) no one piece exceeding 400 to 500 grams in weight, the charcoal must be crushed, and only that portion of it is to be used which will pass through a sieve having 26 meshes to the square centimeter, but which will be retained by a sieve having 81 meshes to the square centimeter. With the said portion of the charcoal a first layer is formed having a depth of about 10 to 15 centimeters; For cementing very large articles; such as for instance armor plates for ships, the charcoal must be employed in pieces of somewhat larger size and the thickness of the first layer must be increasedto, for instancefrom 40 to 50 centimeters. The articles to be cemented are then placed upon the first layer of charcoal, at a distance of from one to two centimeters apart. Any pieces which by reason of their shape or weight, have a tendency to sink into the charcoal, may: be easily supported in position by means of 'a metal netting placed underneath them.

Pieces of flat or elongated form may. be

purpose of obtaining perfect homogeneity" of.

the cemented zone, to fix the articles to be cemented on a rotary shaft of metal or refractory material which extends through thewall of the cementing chamber and can berotated slowly.

. of the improved process I caused to pass through having a depth of 1.4

cementing The pure granulated charcoal prepared as described above, and duly calcined, forms (especially when it has been employed several times in the improved cementation process) a very slippery and movable mass which penetrates with the greatest ease into every recess of the articles to be cemented. This penetration may be promoted by giving slight shakes or shocks to the cementing chamber.

It will be advisable to employ small granulated, charcoal for cementing articles of complicated shape having small recesses, although it hasbeen found that the gas is the essential carburizing medium in the improved cementation process, and that cementation takes place equal-ly'in those parts of the steel articles which are not in contact with the charcoal, but are distant some centimeters from it.

The cementing chamber having been filled in the manner described above, the charging door is closed, and a current of carbon dioxid is caused to circulate slowly through the chamber by means of the pipes already referred to. The speed of the current of carbon dioxid varies also according to the depth of'cementation which it is desired to produce. While the current of carbon dioxid gas is kept uniform, the tem perature of the cementing chamber is raised to bright red heat and is then maintained constant during the entire duration of the cementation which depends-according to fixed definite conditions that are readily determined by preliminary experiments-on the temperature, the speed of the current of gas, and the desired depth of the zone of cementation. I It is impossible to give here particulars suitable for all possible cases, only two of which are given here by way of example in order to show how the results depend on the conditions under which it is performed First example: For cementing according to the improved process at a temperature of 1000 degrees centigrade, articles composed of soft steel (containing 0.07 per cent. of carbon) in order to produce a zone of cementation having a total meters, the current of carbon dioxid must be the chamber for two hours at a speed of about 1 liter per hour for each square .decimeter of the external surface of the steel articles to be cemented.

Second example: By operating at a temperature of 960 degrees (1., but otherwise under the conditions stated in the first example, a zone of cementation is produced mm. The gasesissuing' from the cementing chamber are collected in a suitable gas holder whence they can be caused to circulate anew chamber with an effect similar to depth of 2.5 milli be repeated indefinitely, so thata great saving is effected. When the cementation is complete, the current of gas is stopped, and a trap door in the bottom of the cementing chamber is opened to allow the granulated charcoal to pass out which it does automatically and with the greatest ease owing to its extremely slippery nature; it is received in a suitable receptacle whence it can be poured directly into another cementing chamber. By this means the same charcoal may serve for a very large number of operations, since only the small amount of charcoal which serves directly to carburize the steel of the zones of cemthrough the i eutation, is consumed. After the granular charcoal has been thus removed, the cemented articles remaining in the cementing chamber can be removed readily therefrom for the purpose of being hardened or tempered or subjected to other suitable treatment. When the chamber is empty, the next charge is made directly in the manner described above.

In many cases, and especially when it is desired to produce zones of cementation of great depth without increasing the percentage of carbon therein to a too high degree, it is advisable instead of removing the whole of the granulated charcoal from the cementing chamber in the manner hereinbefore described to remove only the quantity which is necessary to uncover the surface of the articles to be cemented, and then to continue the heating and the circulation of the current of gas in the presence of the charcoal remaining in the cementing chamber. By this means an extraordinarily uniform distribution of carbon in the zone of cementation is obtained, and the carburization may be carried to very great depths (0 or 7 centimeters) without the percentage of carbon in the zone of cementation exceeding the amount produced by the first part of the process. The same result may he produced by leaving the'charcoal in the cementing chamber, and mixing a certain quantity of air with the carbon dioxid during a part or the whole of the cementation. The percentage of carbon in the zones thus produced is lower, .all the other conditions being equal, the greater the proportion of air that is added to the carbon dioxid. Thus for instance in the first example, (cementation during two hours at 1000 degrees C.) by employing pure carbon dioxid a maximum percentage of 0.9 per cent. is produced in the zone of cementation, whereas by employing carbon dioxid mixed with 60 per cent. of air, the maximum percentage of carbon in the zone of cementation is re duced to 0.65 per cent.

In cases where it is desired to produce vzones of cementation having a very high that of the fresh carbon dioxid. This may percentage of carbon (for instance up to 1.3

.cementation. process over existing the furnace.

the cementing material does or 1.5 per cent.), by means of one menting chamber greater or lesser percentage of carbon) of gaseous hydrocarbons such as acetylene, ethylene, gas obtained by the distillation of coal, etc., or liquid hydrocarbons such as benzol, petroleum, etc. The gaseous hydrocarbons, or the vapors which are formed immediately by the liquid hydrocarbons at the temperature of the cementing chamber, mingle with the gases circulating in the apparatus, and have the effect of increasing the percentage of carbon in cementation. In this case it necessary that the articles 'to'be-cemented shall be in contact with the granulated charcoal. In many. cases, in order to produce certain effects, it may be advisable to add air as well as hydrocarbons to the gases employed for cementation. These additions may be made either simultaneously or in succession.

The chief advantages of the improved processes, either as regards its greater facility of execution, or as regards the better results produced by it, are the following 1. e dispensing with the existing inconvenient and expensive cementation boxes, and the use in their place, of a refracto receptacle of the retort type which can be charged and discharged by successive operations without having to be removed from 2. Great saving of cementing material, because the same carbon dioxid gas can be employed over again indefinitely for a long succession of cementing operations, since only the. small quantity of gas is consumed which is lost through leakage, and the whole of the charcoal is utilized in the carburization of the iron or steel. In other words,

not lose its efliciency, is, it never becomes impoverished as is the case with the usual cementing powders), so that it can be used up completely, and noteven the slightest quantity need be thrown away.

3. The speed of penetration ofthe carbon is far greater than that which can be obtained with all is evident.

4-. The extraordinary uniformity of distribution of the carbon in the zones of cementation, which has a very beneficial influence upon the strength of the cemented articles.

5. The possibility of regulating the percentage of carbon in the zones of cementation in such a manner as to keep the maximum percentage below the usual limits certainty the conditions (which vary according to the composition of the steel to be cemented) above which a loss of strength begins to appear, and in all cases theabsolute certainty of being able to avoid, if so desired, the presence of cementite in the zones of cement-ation.

6. The possibility of predetermining with such as temperature, speed of the current of gas, etc., suitable for producing desired results, such as depth of cementation, percentage of carbon, etc.

7. The possibility cementation of very great depths, yond 6 centimeters, without having ever to renew the-cementing material, because, as

of producing zones of th Zones f I stated above, it never becomes impoverished. ]S no longer 8. The absolute certainty of not introducing into the steel any foreign substance other than carbon, which is not thecase with existing cementing powders containing cyanids, organic substances, etc.

9. The complete preservation of the cemented articles, which remain perfectly. as before cementing an article of iron, steel or alloy of steel, wherein I the article to be cemented is heated to a temperature of from about 900 degrees to about 11 00 degs. centigradedn the presence of pure carbon in a state of comparatively fine subdivision and carbon dioxid, whereby said article is provided with a surface layer of any desired depth carburized to any de ree more than the remainder of the artic e,. as set forth.

2. The improved process of cementing an article of iron, steel or alloy of steel, wherein the article to be cemented is packed in pure carbon in a state of comparatively fine subdivision, a current of carbon dioxid passed therethrough whileheating said packed article to a temperature of from about 900 to 1100 degrees centigrade, then after a certain interval, that portion of the ure carbon which is in contact with the surf ces of the article to be cemented is removed, and then the circulation of the carbon dioxid and the heating continued as before, whereby very deep zones of cementation are increasing unduly the percentage of carbon therein, as set forth.

3. vTheimproved process ofcementing an article of iron, steel or alloy of steel, wherein the article to be cemented is packed in granproduced without with the surfaces of ulated charcoal, a current of carbon dioxid passed therethrough while heating said so acked article to a temperature of from about 900 degrees to 1100 degrees centigrade,

then after a certain interval, that portion of the granulated charcoal which is in contact the article to be cemented is removed, and then the circulation of the carbon dioxid and the heating continued as before, whereby very deep zones of cementation are produced without increasing unduly the percentage of carbon therein, as set forth.

at. The improved process of cementing an article of iron, steel or alloy of steel, wherein the article to be cemented is packed in pure carbon in a state of comparatively fine subdivision and a J'current of carbon dioxid passed therethrough with the addition of a certain quantity of air while heating said so acked article to a' temperature of from about QOO-degrees to 1100 degrees centigrade as set'forth. V I

The improved process of cementing an article of iron, steel or alloy of steel, wherein.

1,0eae44 the article to be cemented is packed in granulated charcoal and a current of carbon di oxid passed therethrough with the addition of a certain quantity of air while heating said so packed article to a temperature of from about 900 degrees to 1100 degrees centigrade,as set forth.

6. The improved process of cementing an article of iron, steel or alloy of steel, wherein the article to be cemented is packed in pure carbon in a state of comparatively fine subdivision and a current of carbon dioxid passed therethrough' with the addition of: certain quantities of vaporizable hydrocarbon and air, while heating said so packed article to a temperature of from about 900 degrees to 1100 degrees Centigrade, as set forth.

In testimony whereof I have hereunto set my hand in presence of two subscribing witnesses.

DR. FEDER-ICO GIOLITTI.

Witnesses:

PIERO GIAUOLIO, FEDERICO CARUnvA'ri. 

